Movable ladder

ABSTRACT

A ladder which can be moved across a surface such as a floor, by an occupant while mounted thereon includes a pair of structural units which are disposed adjacent each other and are adapted to rest upon the surface in a stable, upright position with or without an occupant on the ladder. Each unit has a support structure, preferably including a base, which is supported on the surface by wheels, casters, skids, or the like; a supporting frame attached to the base; one or more footrests attached to the support structure; and means for braking each unit and holding it stationary relative to the floor while permitting the other unit to be moved, for example by the occupant. In order to move the ladder the occupant stands with one foot on each unit and brakes one of the units, then moves the second unit in the desired horizontal direction. The occupant then brakes the second unit and moves the first unit into the desired position. When the ladder is in the final location, both units can be braked to provide safety and stability while the ladder is in use.

United States Patent Roylance Feb. 15, 1972 [54] MOVABLE LADDER [21] Appl. No.: 81,898

[52] US. Cl. ..182/15, 182/127, 182/152 [51] Int. Cl. ..E06c U397 [58] Field ofSearch ..182/15,17,127,152

[56] References Cited UNITED STATES PATENTS Primary Examiner-Reinaldo P. Machado Att0rney-Mallinckrodt & Cornaby [57] ABSTRACT A ladder which can be moved across a surface such as a floor, by an occupant while mounted thereon includes a pair of structural units which are disposed adjacent each other and are adapted to rest upon the surface in a stable, upright position with or without an occupant on the ladder. Each unit has a support structure, preferably including a base, which is supported on the surface by wheels, casters, skids, or the like; a supporting frame attached to the base; one or more footrests attached to the support structure; and means for braking each unit and holding it stationary relative to the floor while permitting the other unit to be moved, for example by the occupant. In order to move the ladder the occupant stands with one foot on each unit and brakes one of the units, then moves the second unit in the desired horizontal direction. The occupant then brakes the second unit and moves the first unit into the desired position. When the ladder is in the final location, both units can be braked to provide safety and stability while the ladder is in use.

20 Claims, 10 Drawing Figures Pmmenrm Ian I 3.841.619

SHEET UF'Z INVENTOR. WILLIAM H. ROYLANCE AT TORNE YS MOVABLE LADDER 1. Field This invention relates to movable ladders, and more particularly to ladders which can be moved-about a surface by an occupant mounted thereon.

2. State of the Art Virtually all ladders which are commercially available share one of two common basic designs. They are either designed to be rested against a vertical support, such as a wall, or are capable of supporting themselves on a horizontal surface. A prime disadvantage to ladders of this common construction has been the fact that they could not be moved while the occupant was on the ladder. Although numerous attempts have been made to construct a ladder which could be repositioned without forcing the occupant to dismount, the only qualified success has been a ladder whichis horizontally slideably attached at the upper end thereof to a wall, ledge or the like, while the bottom of the ladder has wheelsso positioned that the ladder can be moved only in parallel relation to the wall while the occupant is still mounted. No. ladders are presently available, however, which can be moved anywhere about a surface with safety and ease by the occupant while mounted on the ladder.

v 3. Objective It was an objective in the development of this invention to provide a ladder construction which could be moved about a surface with safety and-ease by an occupant while mounted on the ladder. e I

SUMMARY OF TI-IEINVENTION According to the invention, a ladder fulfilling this objective comprises a pairof structuralunits which are disposed adjacent each other and adapted to hold an occupant having his feet resting respectively on the two units. The units can be moved horizontally by the occupant relative to each other and relative to the surface over which the ladder is to be moved by alternately. sliding each unit along the surface until the desired position is reached.

Each unit includes a support structure with horizontal dimensions to provide upright stability to the structural unit. In a preferred embodiment the support structure comprises a base member having horizontal dimensions to provide stability to the unit as it rests on the surface and a support frame which is attached to the base and preferably extends upwardly from, the base member to support an occupant standing on lateral foot supports attached to the support frame. In one embodiment, the respective support structures are interconnected through connecting means, such as a bar which is hinged at one or more points along its length and is pivoted on both ends at the points of attachment with each structural unit. Wheels, casters, skids, sliding means, or other low-friction means support the base member upon the surface and provide for relatlvely effortless movement of the structural units across the surface by the occupant. Different surfaces will require different support means to provide the necessary low friction between the means and the surface to enable the units to be moved with case. Of particular importance is the braking means for holding each structural unit stationary relative to the floor. The braking means can be constructed so as to prevent the wheels from moving or can function independently of the wheels to hold the unit motionless relative to the surface.

When the ladder is to be moved, the occupant activates the braking means on one unit and moves the other unit in the desired direction while mounted thereon by sliding the unit along the floor with the force of the occupants foot on the foot support. The second unit is then braked, and the braking means on the first is released. The first unit can then be moved by the occupant into position with the second unit. In this manner, the structural unit can be alternately moved by the occupant into any desired position in safety without the necessity of the occupant dismounting and carrying the ladder to its showing an enlarged new location. When the ladder'is in position, the braking means on both units can be engaged to prevent the ladder from moving while the occupant is using it. It is also contemplated that the units can be powered by'small motors or the like to drive the wheels.

THE DRAWING The best mode presently contemplated for carrying out the invention is illustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view of one embodiment of the ladder showing the support structures enmeshed and discshaped braking means disposed above 'thecasters;

FIG. 2, a perspective view of another embodiment showing a centrally hinged connecting bar pivoted at the points of attachment with the structural units;

FIG. 3, a sectional plan taken along line 3-3 of FIG. 2;

FIG. 4, a sectional elevation taken along line 4-4 of FIG. 3;

FIG. 5, a perspective view of another embodiment illustrating vertically adjustable foot supports;

' FIG. 6, a view in perspective of an alternative embodiment showing handrails attached to each structural unit with brakmg means;

FIG. 7, the portion of FIG. 6 enclosed by dotted line 7, side elevation of an alternative braking means;

FIG. 8, a side elevation of another alternative braking means relating to the embodiment illustrated in FIG. 6;

FIG. 9, a perspective view of still another embodiment showing vertical screws on which the respective foot supports can be raised and lowered by the occupant, and;

FIG. 10, a view in perspective of a folding embodiment of the ladder showing another braking means.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT One embodiment of the invention is illustrated in FIG. 1, in which a ladder corresponding to the invention has a pair of structural units 10, 11 disposed adjacent each other and adapted to rest in a stable manner on a surface 12, such as a floor or the like, with or without an occupant thereon. The units can be constructed of any suitable material, such as metal, plastic, wood fiber glass or combinations thereof. The support structure of unit 10, '11 includes a horizontal base member 13, 14 in the form of a square U, with the openings of the respective Us inverted to accommodate one leg 13a, 14a of the respective adjacent base member. Both structural units can occupy substantially the same floor space in this configuration. The increased lateral dimensions of each structural unit 13, 14 provide enhanced stability'for the units,while permitting units l3, 14 to be disposed in closely spaced relationship to each other. Attached to the respective base members 13, 14 are support frames l5, 16 which in this embodiment comprise a pair of bars 15a, 15b and 16a, 16b respectively, extending upwardly from base members 13, 14 and connected at the upper ends thereof to form a triangular frame. Foot sup ports l7, l8 and 19, 20 extend laterally from the respective triangular frames 15, 16. The foot supports are anchored to frames 15, 16 by means of short extension bars 21.

Base members 13, 14 are supported on surface 12 by a plurality of casters 22 rotatably mounted on the base members at strategic weight-bearing points, e.g., at the corners and ends of the horizontal U-shaped base members. The mounting of casters 22 is preferably accomplished in this embodiment by mounting springs 23 vertically with receptacles 24 and at taching receptacles 24 to the sides of base members 13, 14 at the desired locations. Braking means in this embodiment include braking discs 25 which are fixedly attached to the bottoms of receptacles 24. Casters 22 are rotatably mounted by means of a vertical rod (not shown) extending upwardly through the center of spring 23 to the top of receptacle 24. The vertical rod is longitudinally slideable through the mounting at the top of receptacle 24, so that when pressure is applied to a structural unit 10, 11 such as by the weight of the occupant, discs 25 are forced downwardly into contact with the upper edges of casters 22 to hold casters 22 and the structural unit 10, ll stationary with respect to the floor. Since the pressure on the springs will vary in proportion to the weight of the occupant, it is preferred to utilize adjustable springs to permit spring tension to be varied. Although the braking means are designed to be activated by the downward pressure of the occupants weight other means of actuation are contemplated such as those involving foot or hand manipulations.

When the ladder is in use and braking discs 25 are engaged, for example on one structural unit 10, the other structural unit 11 can be moved horizontally by the occupant to a new position on surface 12. Braking discs 25 on unit 11 are then engaged and the discs 25 on unit are released by shifting the occupants weight from unit 10 to unit 11. Unit 10 can then be moved into the desired position. When both units are in the final desired location, the braking discs on both units can be engaged to prevent the ladder from moving by applying pressure to both units. All of the foregoing can take place without the occupant dismounting from the ladder. The close proximity of the two base members 13, 14 to each other, achieve through the unique base member design, allows the occupant to stand on the foot supports l7, 19 or 18, 20 without taking an uncomfortably wide stance on the ladder. If desired, connecting means, not shown, can be employed between the two units to prevent the units from being moved so far apart that the occupant cannot control both units while mounted thereon.

A second embodiment of the ladder is illustrated in FIGS. 2, 3, and 4, in which the support structure comprises a pair of structural units 30, 31 which include respective base members 32, 33 supported by casters 34. Upright supporting frames 35, 36 extend upwardly from base members 32, 33. Lateral footrests 37 are mounted in ascending relationship on both supporting frames 35, 36. Handrails 38, 39 are provided along the forward upper edges of supporting frames 35, 36 to aid an occupant in mounting and moving the ladder. In this embodiment, both structural units 30, 31 are connected together through connecting means 40, comprising two bars 41, 42 which are pivotally attached at the outer ends of each bar to base members 32, 33. The inner ends of each bar are connected to each other by means of a hinge 43. The pivotal attachment of bars 41, 42 to base members 32, 33 can be accomplished by any effective means and bars 41, 42 can be hinged at one or more places as desired. As illustrated in FIG. 2, the bars are attached to the exteriors of vertical cylinders 44, 45 which are rotatably mounted on upright rods 441, 45a housed in vertical receptacles 46, 47, which are fixedly attached to the respective upper sides of horizontal base members 32, 33. Accordingly, structural units 30, 31 are balanced in an upright position by each other through connecting means 40. The hinged and pivoted connecting means 40 permits each unit 30 or 31 to be moved by an occupant while the other remains stationary through the use of braking means 48, 49, illustrated in detail in FIG. 4. Other connecting means can be employed so long as each unit is permitted to move horizontally with respect to the other. For example, a tube can have one end of a rod longitudinally slideably mounted therein with the outer ends of the tube and the rod pivotally mounted on the respective structural units. Additionally, means such as small stops (not shown), can be attached at appropriate locations to the connecting means or to the base members to prevent the structural units from separating too far in a lateral direction, so as to force the occupant to take an uncomfortably wide stance.

The braking means includes two pairs of upright bars 50, 51 and 52, 53 forming part of supporting structures 35, 36 which slideably extend downwardly through sleeves 54, 55 and 56, 57 (attached to the upper sides of the base members) to the surface 58, and are respectively connected together through horizontal bars 59, 60. Lateral extensions 61 extend inwardly toward the center of the ladder and have small tabs 62 extending downwardly from the bottoms of extensions 61 to make contact with surface 58. Tabs 62 can be constructed of any suitable material, such as plastic, rubber or metal. Sleeves 54, 55 and 57, 58 have small lateral projections or lips 63 on their upper ends which form the base for vertical springs 64. Lateral extensions 65 from bars 50, 51 and 52, 53 form the top of the spring enclosure. As pressure is applied upon supporting frames 35, 36, for example by the weight of an occupant, extensions 65 depress springs 64 against extensions 63 and thereby force tabs 62 securely against surface 58 to brake the structural unit 30 or 31. When the pressure is released, springs 64 force bars 50, 51 or 52, 53 upwardly and lift tabs 62 from contact with surface 58. When tabs 62 are in contact with the surface, they assist in holding the unit in a stable upright position and eliminate some of the lateral pressure on casters 34.

FIG. 5 illustrates a modification of the embodiment shown in FIGS. 2, 3, and 4. The base members 32, 33, the casters 34, braking means and connecting means 40 remain the same, but the supporting frame 35, 36 in each unit comprises a single upright bar 66, 67 on which a foot support 68, 69 is slideably mounted. Both foot supports 68, 69 can be adjusted to any location along the length of bars 66, 67 by appropriate clamping means, thereby obviating the need for a succession of foot supports or elaborate support structure.

The ladder illustrated in FIGS. 6, 7, and 8 comprises yet another embodiment of the invention in which the pair of structural units 70, 71 include the base members 72, 73 which are connected together through connecting means 74, described in detail above in connection with FIG. 2. Base members 72, 73 are supported on the surface by rotatable casters 75. Additional casters can be attached along the interior portion of each base member to aid in supporting the unit on the surface. Foot supports 76 are disposed in ascending order along supporting frames 77, 78. Handrails 79 extend upwardly along supporting frames 77, 78 at about the height of an occupants waist, and are secured to frames 77, 78 through rods 80. Along the top of frames 77, 78 guardrails 81 are attached.

Alternative braking means utilized in this embodiment are detailed in FIGS. 7 and 8. As shown in FIG. 6, flexible bands 82 such as rope brake cables or the like are secured to the upper and lower ends of handrails 79 which are rotatably mounted on rods 80. The bands 82 extend to selected casters 75 mounted on the base members 72, 73 to activate the braking mechanisms shown in FIGS. 7 and 8. In FIG. 7, the band 82 is attached to a bracket 83 which is slideably mounted through a base member 73. Caster 75 is attached to the bottom of bracket 83 with the wheel thereof normally braked against the bracket. A spring 84 is disposed between the bottom of bracket 83 and base member 73. As handrail 79 is rotated, for example by the hand of an occupant, band 82 is pulled upwardly, which raises bracket 83 against spring 84, thereby releasing caster 75 to roll freely across surface 85. The braking means on the opposite structural unit remains locked in place until the handrail is rotated to release bracket In FIG. 8, caster 75 is rotatably mounted directly on base member 73. The braking means comprises a rod 86 extending upwardly through an aperture in base member 73 and connected at one end of a lateral extension member 87. A spring 88 is disposed longitudinally about rod 86 between extension 87 and the upper side of base member 73. Attached to the other end of extension 87 is a flexible band 82 which extends downwardly through a U-shaped channel 88 in base member 73 adjacent rod 86, and upwardly from base member 73 to handrail 79. In this embodiment, as the handrail 79 is rotated the braking means is activated to force rod 86 downwardly into contact with surface 85, thereby braking the structural unit and locking the unit in place. It should be understood that as many of these braking means can be utilized with the casters as is necessary to effectively brake each unit.

An additional embodiment of the invention is illustrated in FIG. 9, in which the pair of structural units 90, 91 include respective base members 92, 93, comprising single horizontal bars supported upon rotatable casters 94 disposed at each end of the base members. Stability with respect to the surface is provided by connecting means 95, similar in design and function to the connecting means 40 described in connection with FIG. 2 above. Support means for the respective units include a pair of upright bars 96, 97, and 98, 99 with each pair being connected at the upper ends thereof by a lateral bar 100, 101 held by brackets 100a, 100b and 101a, 101b surrounding bars 96, 97, and 98, 99. As a safety device and to aid in moving the ladder, crossbars 102, 102a and 103, 103a extend horizontally from brackets 100a, 100k and 101a, 101b to enclose the area occupied by the occupant when the ladder is in use. The crossbars are pivoted inwardly on the brackets and can be moved inwardly to enable an occupant to mount the ladder, then can be returned to their original position.

The braking means and foot supports in this embodiment comprise an integral unit in which a pair of foot supports 104 are slideably mounted respectively between upright bars 96, 97 and 98, 99, so as to permit vertical movement along the length of the bars. Rotatable bearings 105, 106 are disposed near the outer edge of the respective foot supports. Bearings 105, 106 are threaded along their interior circumference to receive and hold threaded screws 107, 108 which extend upwardly from spring means 109, 1 attached to the upper ends of vertical members 111, 112 extending upwardly from base members 92, 93. Vertical members 111, 112 are hollow and have a rod (not shown) extending upwardly from respective braking members 113, 114 through vertical members 111, 112 and springs 109, 110 and attached to the lower ends of threaded screws 107, 108.

In operation, the height of the foot supports 104 is conveniently adjusted by rotating bearings 105, 106, for example with the foot of the occupant, so that the foot supports are raised or lowered along the supporting means. The braking members 113, 114 are activated by bringing pressure to bear on the foot supports, for example by the occupant shifting his weight to one foot support. As the foot support is depressed, the threaded screw is depressed against the spring which forces the interior rod downward and lodges the braking member against the surface.

FIG. 10 illustrates an embodiment of the invention which can be folded when not in use for convenient carrying and storage requiring little storage space. The pair of structural units 120, 121 include respective support structures 123, 124 connected together by means of the connecting means 122, similar to those described above in connection with FIGS. 2, 5, and 9. In each unit, support structure 123, 124 rests on rotatable casters 125 disposed at each lateral end thereof. Lateral support platforms 126, 127 and 128, 129 are attached one over the other to respective structures 123, 124 along one side of each platform by means of hinges 130. Along opposite sides of platforms 126, 127, and 128, 129 are upright frames 131, 132 also attached to the platforms by means of hinges 133. Upright frames 131, 132 are normally raised slightly above the surface through the lifting action of vertical springs 134 disposed at the interior angles formed between platforms 126, 127 and 128, 129 and structures 123, 124. An occupants weight on either platform 128 or 129 will cause structural unit 121 to lower the frame 132 to the surface, thereby holding the unit in place while unit 120 is moved into the desired location. When the depressed unit 121 is released, springs 134 force platforms 128, 129 upwardly to raise frame 132 from the surface. Frames 131 and 132 can have friction caps 135 of plastic, rubber or the like at the points of contact with the surface to provide increased holding power. For storage or carrying purposes, the ladder can be folded into a compact, flat package by simply raising platforms 126, 127 and 128, 129 and frames 131 and 132 vertically until the platforms are on edge, and then move the two structural units together. Handles or the like can be provided.

Whereas this invention is here illustrated and described with respect to certain preferred forms thereof, it is to be understood that many variations are possible without departing from the inventive concepts particularly pointed out in the claims. For example, other springing means than simple springs can be employed in the ladder; also the foot supports or steps can be arranged in any desired configuration. Moreover, any braking means can be employed which is adapted to effectively brake the structural unit relative to the surface over which the ladder is to be moved. A variety of connecting means are employable so long as they permit the two units to be moved relative to each other. Some embodiments may rely on the connecting means as support for each unit to achieve stability with respect to the surface. Other embodiments have structural units which rest stably on the surface without reliance therefor on the connecting means. Also, platforms or other means can be attached to the ladders to hold boxes, paint buckets, and the like in convenient proximity to the occupant while working on the ladder.

I claim:

1. A ladder adapted to be moved horizontally about a surface by an occupant mounted thereon, comprising a pair of structural units disposed adjacent each other and adapted to rest in stable upright relation to the surface and to permit horizontal movement relative to each other, each structural unit comprising in combination:

support structure having horizontal dimensions which provide the structural unit with stability when disposed upon the surface;

at least one lateral foot support structure; means attached to the support structure for supporting the structure upon the surface and adapted to permit lowfriction motion of said unit across the surface; and

braking means, operable by the occupant, for holding the structural unit stationary with respect to the surface, while permitting the other structural unit to be moved relative thereto.

2. A ladder as set forth in claim 1, wherein the support attached to the support structure comprises a base member having horizontal dimensions and a supporting frame attached to the base member.

3. A ladder as set forth in claim 2, wherein the base members of the structural units comprise horizontal U-shaped members in inverted relationship to each other so that one arm of each member fits within the other base member, thereby permitting the foot supports on each structural unit to be disposed in proximate stable relationship to each other.

4. A ladder as set forth in claim 1, wherein the structural units can be intermeshed with each other so that both units occupy substantially the same space when disposed upon the surface, thereby permitting the foot supports to be disposed in proximate stable relationship to each other.

5. A ladder as set forth in claim 1, wherein the low-friction supporting means comprise wheels rotatable in any lateral direction.

6. A ladder as set forth in claim 5, wherein the braking means comprises a spring-loaded disc disposed above each wheel, said disc adapted to engage the wheel when actuated to prevent the wheel from moving.

7. A ladder as set forth in claim 1, wherein the braking means includes spring means for actuating a braking member.

8. A ladder as set forth in claim 7, wherein the spring means can be adjusted to regulate resiliency.

9. A ladder as set forth in claim 1, wherein each structural unit has a handrail.

10. A ladder as set forth in claim 1, wherein each structural unit has a plurality of foot supports disposed in ascending relationship with each other.

11. A ladder as set forth in claim 1, wherein each structural unit has a single foot support which is vertically adjustable.

12. A ladder as set forth in claim 11, wherein the foot supports are adapted to be raised and lowered by means of the occupants foot.

13. A ladder as set forth in claim 1, wherein the braking means is adapted to be actuated by the weight of the occupant.

14. A ladder as set forth in claim 1, wherein the braking means is adapted to be actuated by hand manipulations of the occupant.

15. A ladder as set forth in claim 1, wherein the braking means include a brake member disposed interiorly of each structural unit, and adapted to engage the surface and to support the unit in an upright position when activated.

16. A ladder as set forth in claim 1, including means for defining the outer limits of the lateral distance between the two structural units.

17. A ladder as set forth in claim 1, wherein the pair of adjacent structural units are interconnected through connecting means, said connecting me s adapted to pennit the structural units to be moved horizontally relative to each other.

18. A ladder as set forth in claim 17, wherein the structural units support each other in an upright position through the connecting means.

19. A ladder as set forth in claim 17, wherein the connecting means is pivotable about each structural unit and is hinged at at least one point between the two structural units.

20. A ladder as set forth in claim 17, wherein the connecting means comprise a tube having a rod longitudinally slideably mounted therein with the outer end of the tube pivotably mounted on one of the structural units and the outer end of the rod pivotably mounted on the other unit.

1' i i i 

1. A ladder adapted to be moved horizontally about a surface by an occupant mounted thereon, comprising a pair of structural units disposed adjacent each other and adapted to rest in stable upright relation to the surface and to permit horizontal movement relative to each other, each structural unit comprising in combination: support structure having horizontal dimensions which provide the structural unit with stability when disposed upon the surface; at least one lateral foot support attached to the support structure; means attached to the support structure for supporting the structure Upon the surface and adapted to permit low-friction motion of said unit across the surface; and braking means, operable by the occupant, for holding the structural unit stationary with respect to the surface, while permitting the other structural unit to be moved relative thereto.
 2. A ladder as set forth in claim 1, wherein the support structure comprises a base member having horizontal dimensions and a supporting frame attached to the base member.
 3. A ladder as set forth in claim 2, wherein the base members of the structural units comprise horizontal U-shaped members in inverted relationship to each other so that one arm of each member fits within the other base member, thereby permitting the foot supports on each structural unit to be disposed in proximate stable relationship to each other.
 4. A ladder as set forth in claim 1, wherein the structural units can be intermeshed with each other so that both units occupy substantially the same space when disposed upon the surface, thereby permitting the foot supports to be disposed in proximate stable relationship to each other.
 5. A ladder as set forth in claim 1, wherein the low-friction supporting means comprise wheels rotatable in any lateral direction.
 6. A ladder as set forth in claim 5, wherein the braking means comprises a spring-loaded disc disposed above each wheel, said disc adapted to engage the wheel when actuated to prevent the wheel from moving.
 7. A ladder as set forth in claim 1, wherein the braking means includes spring means for actuating a braking member.
 8. A ladder as set forth in claim 7, wherein the spring means can be adjusted to regulate resiliency.
 9. A ladder as set forth in claim 1, wherein each structural unit has a handrail.
 10. A ladder as set forth in claim 1, wherein each structural unit has a plurality of foot supports disposed in ascending relationship with each other.
 11. A ladder as set forth in claim 1, wherein each structural unit has a single foot support which is vertically adjustable.
 12. A ladder as set forth in claim 11, wherein the foot supports are adapted to be raised and lowered by means of the occupant''s foot.
 13. A ladder as set forth in claim 1, wherein the braking means is adapted to be actuated by the weight of the occupant.
 14. A ladder as set forth in claim 1, wherein the braking means is adapted to be actuated by hand manipulations of the occupant.
 15. A ladder as set forth in claim 1, wherein the braking means include a brake member disposed interiorly of each structural unit, and adapted to engage the surface and to support the unit in an upright position when activated.
 16. A ladder as set forth in claim 1, including means for defining the outer limits of the lateral distance between the two structural units.
 17. A ladder as set forth in claim 1, wherein the pair of adjacent structural units are interconnected through connecting means, said connecting means adapted to permit the structural units to be moved horizontally relative to each other.
 18. A ladder as set forth in claim 17, wherein the structural units support each other in an upright position through the connecting means.
 19. A ladder as set forth in claim 17, wherein the connecting means is pivotable about each structural unit and is hinged at at least one point between the two structural units.
 20. A ladder as set forth in claim 17, wherein the connecting means comprise a tube having a rod longitudinally slideably mounted therein with the outer end of the tube pivotably mounted on one of the structural units and the outer end of the rod pivotably mounted on the other unit. 